The risk that a patient will be given blood that is infected with HIV, the virus that causes AIDS, is less than 2 cases per million units transfused, according to researchers participating in the National Heart, Lung, and Blood Institute's (NHLBI) Retrovirus Epidemiology Donor Study (REDS). The risk for other transfusion-transmitted viruses is also low, the study found.
REDS is the first study to simultaneously examine the risk of transmission of four of the blood-borne viruses of greatest concern to those with responsibility for blood safety in this country. The viruses are HIV, HTLV, and Hepatitis B and C.
In a paper published in the June 27th issue of the New England Journal of Medicine, the researchers report that the greatest transfusion-associated risks are from hepatitis B and C. The transfusion-associated risk of hepatitis B is approximately 8 times greater than that of HIV, while the risk of hepatitis C is 5 times greater.
These agents are more often missed by current screening tests than HIV and HTLV because the time between when the donor is infected and when the antibodies to the virus appear in sufficient quantity in the blood to be detected by current screening tests, the "window period," is longer than that for HIV and HTLV. While hepatitis B and C can result in serious liver damage, HIV is far more deadly.
The study also found that development of new and more sensitive viral-antigen or nucleic acid screening tests, which do not rely on the development of antibodies, could substantially reduce the transfusion-associated risk of hepatitis B and C.
According to NHLBI Director Dr. Claude Lenfant, "The NHLBI has a commitment to improving the safety of the blood supply. The REDS study is a major tool in our ongoing efforts to reduce the risk of current and potential infectious agents in the blood and to identify methods to exclude donors at risk. This new study from REDS provides an important mechanism for evaluating the threat of "window period" blood donations. And it validates our efforts to develop more sensitive nucleic-acid based screening tests that will reduce or eliminate the threat of "window period" donations."
In the past, estimates of the risk of transmission of infectious diseases through blood donations have been based on the frequency, or prevalence, of infectious diseases in people who contracted the disease through transfused blood. These data present a picture of the percentage of people who may have been infected in the past. The technique for estimating risk developed by the REDS investigators provides more accurate information about the ongoing risk of new infected blood units entering the blood supply.
The REDS investigators analyzed data on more than 586,000 people who donated blood more than once between 1991 and 1993 at 5 major urban blood centers nationally. The total number of donations reviewed was more than 2.3 million. Since virtually all transfusion-transmitted infections occur today as a result of "window period" donations, the researchers examined records of those donors who donated at least one unit of blood that tested negative for the four viruses but who subsequently donated a unit of blood found to be contaminated with one of the four viruses.
The Retrovirus Epidemiology Donor Study (REDS) was initiated in 1989 to provide the NHLBI with a mechanism for monitoring the incidence of retroviruses and identifying potential new infectious agents among volunteer blood donors. It compiles data on the characteristics and test results of blood donors to identify donors at risk for infection and maintains a serum repository of donor samples for further study. It is funded by the NHLBI through monies from the NIH Office of AIDS Research. It is carried out by investigators at the Irwin Memorial Blood Centers in San Francisco, the Oklahoma Blood Institute in Oklahoma City; and American Red Cross Blood Services in the Baltimore-Washington, DC, Detroit, and Los Angeles areas. Westat, Inc. in Rockville, MD is the coordinating center.
The NHLBI, which is part of the National Institutes of Health, is one of three federal agencies with responsibilities related to blood safety. The federal Centers for Disease Control and Prevention and the Food and Drug Administration are charged with monitoring and regulating blood safety respectively, while the NHLBI supports fundamental research, including studies of disease transmission through transfusion, development of methods to inactivate viruses in donated blood, improvement of blood donor screening procedures, research to reduce human error in transfusion medicine, and studies of emerging diseases that may be transmitted by blood transfusion.